Semiconductor manufacturing apparatuses used to manufacture a semiconductor device, such as a semiconductor integrated circuit, include a thermal processing apparatus that performs film deposition to a semiconductor wafer, a plasma etching apparatus, a liquid processing apparatus that performs resist coating and development, etc. With the recent decrease in the line width and the thickness of a pattern, the yield is largely affected by a slight abnormality occurring in the apparatus. Therefore, it is necessary to detect an abnormality in the apparatus exactly and quickly.
An abnormality of a semiconductor manufacturing apparatus will be explained below referring to a batch-type thermal processing apparatus as an example. In a vertical low-pressure CVD (chemical vapor deposition) apparatus, a holder for holding substrates in a shelf-like manner is loaded into a reaction tube, vacuum pumping is performed through an exhaust pipe while supplying a process gas in the reaction tube, and the inside of the reaction tube is uniformly heated by a heater located around the reaction tube to perform a deposition process. If the airtightness of the reaction tube is degraded, outside air enters the reaction tube disturbing scheduled pressure control and adversely affecting deposition process. Therefore, it is necessary to promptly detecting the abnormality and to perform maintenance. The airtightness may possibly be degraded by a deteriorated resin seal member provided on a lid in the reaction tube or a defective sealing mechanism provided on a revolving shaft passing through the lid.
Pressure control in the reaction tube is performed by controlling the opening of a pressure control valve, such as a butterfly valve, which is provided in the exhaust pipe. If the airtightness in the reaction tube is degraded, it is necessary to discharge an extra amount of air corresponding to the amount of outside air entering into the reaction tube, resulting in an increased opening of the pressure control valve. The opening of the pressure control valve is monitored by a computer. If the opening exceeds a threshold value, the computer judges that the airtightness of the reaction tube has degraded (an abnormality of the apparatus has occurred).
However, since reaction products also adhere to the inner wall surface of the exhaust pipe through the deposition process, the conductance of the exhaust pipe decreases, resulting in an increased opening of the pressure control valve to obtain the same pressure. Therefore, if the cumulative film thickness increases, the opening exceeds the threshold value, and accordingly the computer judges that an apparatus abnormality has occurred. If the threshold value of the opening is set to a large value in order to avoid such misjudgment, a problem of overlooking abnormal airtightness of the reaction tube arises. Furthermore, if the cumulative film thickness excessively increases, the conductance of the exhaust pipe decreases too much, disturbing sufficient evacuation to a predetermined degree of vacuum. Under such a situation, cleaning is required. An alarm for prompting cleaning is made if the valve opening exceeds a predetermined threshold value. However, as mentioned above, if abnormal airtightness of the reaction tube occurs, there arises a problem that the valve opening exceeds the threshold value for judgment criteria of cleaning.
The foregoing problems of abnormality detection may occur also in other portions. Conventionally, the heater composed of resistance heating elements arranged around the reaction tube has been replaced after a predetermined operating hour has elapsed. However, if the heater fails before the predetermined operating hour has elapsed, thermally processed wafers will become defective. Since a 12-inch size wafer is very expensive, economical loss is large. Furthermore, the heater of the batch-type furnace is expensive because not only of the constituent material having high durability and low contamination but also of an increased size with increasing diameter of substrates. On the other hand, a heater maker determines a guaranteed operating hour with a certain margin. Actually, in many cases, the heater is replaced in spite of its remaining life, resulting in an increased running cost of the apparatus.
As mentioned above, such a semiconductor manufacturing apparatus has a problem that a defective component thereof cannot certainly be detected and therefore an operable component is replaced or maintained on an early stage.
JP2002-352938A discloses a method of predicting a life of a heater for a vertical thermal processing apparatus. However, the method disclosed here can determine an abnormality based on a tendency of variation in a power value that has been monitored for a prolonged period of time; the method can neither detect an apparatus failure in real time or almost in real time nor determine correctly whether a failure occurred in the heater itself or in other component parts.